1. Field of the Invention
The present invention relates to a method of driving a display device and to a display device using the driving method, and more particularly to a method of driving an active matrix semiconductor display device having thin-film transistors (TFTs) fabricated over an insulating substrate. In addition, the present invention relates to an active matrix semiconductor display device using the driving method, and more particularly to an active matrix liquid crystal display device which is one type of active matrix semiconductor display device. The present invention is also applicable to a passive matrix type display device.
2. Description of Related Art
The art of forming semiconductor thin films over an inexpensive glass substrate and fabricating thin-film transistors (TFTs) has recently been making rapid progress. The reason for this is that a demand for active matrix liquid crystal display devices (liquid crystal panels) has been increasing.
In general, in an active matrix liquid crystal display device, pixel TFTs are respectively arranged in at least several tens of pixel areas up to a maximum of several millions of pixel areas which are arranged in a matrix form (this circuit is called active matrix circuit), and electric charges which flow into and out of pixel electrodes located in the respective pixel areas are controlled by the switching function of the pixel TFTs.
The active matrix circuit has conventionally used thin-film transistors which use amorphous silicon formed over a glass substrate.
An active matrix liquid crystal display device which uses thin-film transistors using a polycrystalline silicon film formed over a quartz substrate has recently been realized. In this case, a peripheral driving circuit for driving pixel TFTs can be fabricated on the same substrate as an active matrix circuit.
The art of using a technique such as laser annealing to form a polycrystalline silicon film over a glass substrate and fabricate thin-film transistors is also known. The use of this art makes it possible to integrate an active matrix circuit and a peripheral driving circuit on one glass substrate.
In recent years, active matrix liquid crystal display devices have been widely used as display devices for personal computers. In addition, large-screen active matrix liquid crystal display devices have been becoming used in not only notebook types of personal computers but also desktop types of personal computers.
In addition, attention is becoming drawn to projectors using small-sized active matrix liquid crystal display devices having high definition, high resolution and high image quality. Among such projectors, projectors for high-definition televisions which can display higher-resolution video images are drawing more attention.
CRTs have heretofore been used in the above-described personal computers and projectors. However, if CRTs are used, problems such as power consumption, volume and weight become serious according to the requirements for the sizes and resolutions of screens. For this reason, it has been considered that the aforesaid active matrix liquid crystal display devices replace CRTs which have heretofore been primarily used. However, it has been pointed out that if a conventional active matrix liquid crystal display device and a CRT display images at the same resolution, the conventional active matrix liquid crystal display device is lower in horizontal resolution than the CRT.
FIG. 22 shows a video image of a resolution measuring chart relative to a CRT, while FIG. 23 shows a video image of a resolution measuring chart relative to a rear projector using a conventional active matrix liquid crystal display device. The CRT and the active matrix liquid crystal display device had a resolution of SXGA (1240×1024 pixels). When both video images are compared, it will be seen that the video image, shown in FIG. 23, of the rear projector using the conventional active matrix liquid crystal display device is lower in horizontal resolution than the video image of the CRT which is shown in FIG. 22 (as indicated by an arrow in FIG. 23).
As described above, the conventional active matrix liquid crystal display devices are lower in horizontal resolution than CRTs which conform to the same standards, so that it is difficult for the conventional active matrix liquid crystal display devices to reproduce images with high quality similar to that of CRTs.
Passive matrix liquid crystal display devices are regarded as inferior in image quality to active matrix liquid crystal display devices, but, in various fields, there are demands for passive matrix liquid crystal display devices in that they are simple in structure and inexpensive. However, the current passive matrix liquid crystal display devices have not yet achieved image quality comparable to that of active matrix liquid crystal display devices.